This invention relates generally to powered surgical handpieces and, more particularly, to a powered surgical handpiece with a membrane switch that provides an audible and tactile indication of when the switch undergoes a state transition.
In modern surgery, one of the most important instruments available to medical personnel is the powered surgical handpiece. Typically, this handpiece includes a housing that is held by a surgeon. Inside the handpiece is some type of power-generating unit. Often, this unit is a motor. However, the power-generating unit can also be a transducer that generates sonic energy or a light-emitting device that generates thermal energy. Usually some type of accessory is attached to the head end, also known as the distal end, of the handpiece. The accessory serves as the component that transfers the energy developed by the power-generating unit to the surgical site in order to accomplish the desired surgical procedure. For example burs, drill bits and shavers are attached to handpieces that contain motors. The motor rotates these accessories in order to cause the selected removal of tissue to which they are applied. Sonic and optical waveguides are attached to the distal ends of the handpiece that, respectively, have sonic and light generating units. These waveguides direct the energy that is transmitted through them to surgical sites so that the energy causes the desired end surgical affect.
The availability of powered surgical handpieces has made it possible to perform surgical procedures more quickly and more accurately than was previously possible with the manual handpieces that they replaced. Moreover, the availability of some powered surgical handpieces has made it possible to perform some surgical procedures that, previously, were difficult, if not impossible, to perform.
When constructing a powered surgical handpiece, it is often desirable to mount switches on the surface of the housing. Often, but not always, these switches are connected to a control console to which the handpiece is connected. The depression of the switches result in the change of the characteristics of the power signal that the control console applies to the handpiece""s power generating unit. The modulation of this power signal causes the power generated by the handpiece to undergo a user-requested state change. These switches make it possible for the surgeon to, with a single hand, both control the position of the handpiece and the operation of its power-generating unit. Still another advantage of providing these switches is that they eliminate the need for the surgeon to have to verbally give commands to a technician who, in turn, manipulates switches or knobs on the control console in order to cause the desired state change of the handpiece power generating unit.
Currently, many handpieces are provided with carbon contact switch assemblies. This type of assembly includes a substrate. Each switch on the substrate includes two conductive surfaces that are separate from each other by a relatively small distance of 0.100 inches or less. A rubber or silicon rubber sheet is fitted over the substrate. This sheet forms the exposed outer body of the switch assembly. For each switch on the assembly, the rubber sheet is formed to have a raised boss that forms the portion of the switch that is manually depressed. This boss subtends the complementary conductive surface of the switch with which it is integral. A conductive member is mounted to the underside surface of the rubber sheet opposite the raised boss. This conductive member may be a carbon embedded pad or a disk of metal that is highly conductive. Normally, the conductive member is spaced away from the adjacent conductive surfaces on the substrate. However, the depression of the boss causes the rubber sheet to flex inwardly. This displacement of the rubber sheet results in the conductive pad coming into physical contact with the underlying, closely spaced conductive surfaces. As a result of this contact, the conductive pad completes the circuit between the substrate conductive surfaces. The completion of this circuit thus closes the connection controlled by the switch.
A disadvantage of the above described switch assembly is that the feedback it provides upon its transition from the open state to the closed state is nominal. Consequently, it is difficult for the surgeon to know whether or not the power generating unit has actually received a set of signals requiring it to undergo the state change the surgeon wanted to occur when he/she actuated the switch. Sometimes, because the surgeon did not know whether or not the switch was actuated, he/she may repeatedly depress the switch. This action can result in the handpiece power-generating unit undergoing state changes in excess of what the surgeon wanted.
It has been suggested that it would be useful to provide powered surgical handpieces with membrane type switches. A membrane switch has a small, flexible metal dome that is located over the complementary conductive surfaces on the underlying substrate. The flexing of the dome results in the dome establishing an electrical connection between the conductive surfaces on the substrate. Also, when the dome is flexed, a distinct xe2x80x9cclickxe2x80x9d sound is heard and a distinct tactile is obtained by the person that depressed it. Collectively, this audible and tactile feedback provides the surgeon with an indication that the switch has closed the connection it is intended to establish.
However, to date, it has proven difficult to provide a handpiece with a membrane switch assembly. This is because, in order to be reused, a surgical handpiece is typically subjected to autoclaving in order to sterilize it. In autoclaving, the handpiece is placed in a chamber in which it is exposed to saturated steam which has a temperature of approximately 270xc2x0 F. and is at a pressure of approximately 30 psi. This high temperature water vapor flows into most of the unsealed portions of the handpiece. If the metal parts forming a membrane switch are exposed to this water vapor, they will, in a relatively short time period, corrode. Moreover, when the other components of a membrane switch assembly are exposed to high temperatures, even in the absence of water vapor, they are likewise prone to break down. Consequently, while there have been some efforts to provide powered surgical handpieces with membrane switch assemblies, the end products have not proven particularly satisfactory.
This invention is related to a powered surgical handpiece with a membrane-type switch assembly. The individual switches of the assembly provide tactile feedback when the switches are depressed. The switch assembly of this invention is able to withstand the rigors of the sterilization process with the handpiece with which the assembly is integral.